1. Field of the Invention
This invention relates to data recording apparatus and, more particularly, to such apparatus capable of accurate and reproducible positioning of the read-write transducers incorporated in such apparatus.
2. Description of the Prior Art
Magnetic recording is a common method for storing both analog and digital information or data. Today, in the digital field particularly, recording of data on the surfaces of magnetic discs is a widely-used technique. The recording and playback are effected by well-known techniques involving electromagnetic transducers, more commonly referred to as "read-write heads". In the case of digital data recording these heads, in the record mode, make a magnetic imprint on the surface of the disc each time an electrical pulse, corresponding to a bit, is impressed upon the head. Because the disc is rotating and the head is stationary at the moment of recording any particular bit, successive bits are recorded along "tracks". A digital recording disc may have on the order of 200 concentric tracks or more, depending on the resolution of the read-write heads. The spacing of these concentric tracks becomes very small as the number of tracks increases. To extract electrical signals from the disc bearing the recorded signals it is necessary to position the head in the read mode exactly over the center of the track which was made by that same head or by a corresponding head during the write mode. Such a track may be only 0.005 in. in width with comparable inter-track spacing, thus requiring a high degree of head positioning accuracy.
Because rapid access to such recorded data is an essential characteristic for any computer system, the location of a recorded track must not only be accurate, but it must be rapid. Computer manufacturers specifiy a maximum time of a few milliseconds for movement from one track to another. Furthermore, the sequence of head shifting from one track to another can be almost continuous, resulting in severe design requirements on the apparatus in the areas of stability, reproducibility, ruggedness and freedom from frequent preventive or corrective maintenance.
The device normally used for effecting the positioning of the read-write heads is a linear motor or linear actuator which operates on the same basic principle as the voice coil in a loudspeaker and is thus commonly referred to as a voice-coil positioner or actuator.
The prior art discloses various methods and means for combining linear actuators with head positioning apparatus in data recorders. For example, U.S. Pat. No. 3,656,015 of Donald E. Gillum discloses a linear motor actuating a read-write head carriage which is guided by means of an upper and a lower rail along which a single grooved upper wheel and a pair of such grooved lower wheels ride during motion of the carriage. Such a suspension system has a very limited bearing surface and, as a result, that bearing surface will wear severely, and stable motion of the head carriage and accurate positioning of it will become difficult. Further, in an attempt to reduce wear, lubrication of the rails may be required. This additional maintenance step and the problems associated with it are eliminated in the present invention. U.S. Pat. No. 3,470,399 of Johnson et al shows a linear-motor-driven positioner utilizing a male dovetail member for carriage guidance. Such a structure is bulky and not usable where compactness is essential in the product. Other patents of interest in connection with linear positioners for magnetic transducers are U.S. Pat. Nos. 3,665,443 of Gillum et al., 3,586,891 of Applequist and 3,521,092 of Kalthoff.
None of the known prior art describes or suggests how to perform the goals achieved by the present invention. The devices of the prior art either are too bulky or too inaccurate to achieve the goals sought and achieved by the present invention.
Accordingly, it is a general object of the present invention to provide improved linear positioner apparatus.
It is a further object of the present invention to provide linear positioner apparatus which achieves maximum stability and accuracy in positioning with maximum compactness in the apparatus.
It is a more specific object of the present invention to provide linear positioner apparatus which is compact, accurate in its positioning in response to control signals, and free from maintenance problems.